"Welcome to the world, Penelope Scott Disick!" she wrote. "Kourtney gave birth to a beautiful baby daughter on Sunday and the whole family is so thrilled to finally meet her!"

Describing Penelope as "absolutely perfect", she continued: "I am so excited to be an aunt again and can't wait to spoil little Penelope. I know Mason is going to be the best big brother in the whole world. Congratulations Kourtney and Scott. Xo"

Kourtney has previously released a statement saying that she is "overjoyed" about the birth of her daughter.